Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

On a liquid crystal panel, plural areas whose number is larger than that
of temperature sensors are defined. In a memory, temperature relation
information representing a relation between an output value of a
temperature sensor and a temperature of each of the plural areas is
stored. A controller acquires the output value of the temperature sensor
and estimates, based on the temperature relation information and the
acquired output value, the temperature of each of the plural areas.
According to this configuration, the temperature of each of the plural
areas defined on the liquid crystal panel can be obtained with a small
number of temperature sensors.

Claims:

1. A liquid crystal display device comprising: at least one temperature
sensor; a liquid crystal panel having a plurality of areas defined
thereon, wherein number of the plurality of areas is larger than that of
the at least one temperature sensor; a memory having temperature relation
information stored therein in advance, the temperature relation
information representing a relation between an output value of the at
least one temperature sensor and a temperature of each of the plurality
of areas; and a controller which receives an output value of the at least
one temperature sensor and estimates, based on the temperature relation
information and the received output value of the at least one temperature
sensor, a temperature of each of the plurality of areas.

2. The liquid crystal display device according to claim 1, wherein the
controller uses a plurality of relation formulas defined by the
temperature relation information to thereby estimate the temperatures of
the plurality of areas, wherein each of the plurality of relation
formulas represents the relation between the output value of the at least
one temperature sensor and the temperature of each of the plurality of
areas.

3. The liquid crystal display device according to claim 2, wherein the
memory has a plurality of coefficients stored therein as the temperature
relation information, the plurality of coefficients is associated with
the plurality of areas respectively, and the plurality of relation
formulas are defined by a fundamental relation formula to which the
plurality of coefficients are applied, respectively.

4. The liquid crystal display device according to claim 3, wherein the
fundamental relation formula includes, as its variables, a latest output
value of the at least one temperature sensor and a value based on a
preceding output value of the at least one temperature sensor.

5. The liquid crystal display device according to claim 4, wherein the
fundamental relation formula includes Infinite Impulse Response Filter
function which includes, as its variables, the value based on the
preceding output value of the at least one temperature sensor.

6. The liquid crystal display device according to claim 1, wherein the
controller determines, based on information changing according to an
elapsed time since the start of driving of the liquid crystal display
device, whether or not a present time falls in a steady-state period
about temperature of the liquid crystal panel, and the controller
executes a first process for estimating temperatures of the plurality of
areas when the present time falls in the steady-state period, and
executes a second process for estimating temperatures of the plurality of
areas when the present time does not fall in the steady-state period.

7. The liquid crystal display device according to claim 6, wherein two
temperature sensors disposed away from each other are included as the at
least one temperature sensor, and the controller uses, as the information
changing according to the elapsed time since the start of driving of the
liquid crystal display device, a difference in output value between the
two temperature sensors.

8. The liquid crystal display device according to claim 1, further
comprising a backlight unit including a light guide plate and a light
source disposed at least one side of the light guide plate.

9. The liquid crystal display device according to claim 8, further
comprising a circuit board having the at least one temperature sensor
attached thereon and disposed along the at least one side of the light
guide plate.

10. The liquid crystal display device according to claim 9, further
comprising a rear frame made of metal and covering the rear side of the
backlight unit, wherein the circuit board is fixed to the rear frame.

11. The liquid crystal display device according to claim 8, further
comprising a plurality of circuit boards, wherein the at least one
temperature sensor is attached to one of the plurality of circuit boards
which is closest to the light source.

12. The liquid crystal display device according to claim 8, wherein the
light source is composed of a plurality of LEDs.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority from Japanese application
JP2011-052650 filed on Mar. 10, 2011, the content of which is hereby
incorporation by reference into this application.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a liquid crystal display device
including a temperature sensor for obtaining temperature information of a
liquid crystal panel.

[0004] 2. Description of the Related Art

[0005] As disclosed in JP 2000-356976 A, a liquid crystal display device
including a temperature sensor for detecting temperature of a liquid
crystal panel has been proposed in the related art. Temperature
information of the liquid crystal panel is used, for example, to correct
the gray-scale value of each pixel.

SUMMARY OF THE INVENTION

[0006] The temperature of a liquid crystal panel sometimes varies
depending on positions on the liquid crystal panel. For example, in a
liquid crystal display device including a backlight unit having a light
source at the edge of the backlight unit, the temperature of a portion
(area) close to the edge of the liquid crystal panel is easily increased
compared to those of the other areas. If the temperature of each area can
be detected, control with higher accuracy is possible. However, when the
same number of temperature sensors as areas are used, the cost of the
liquid crystal display device is increased.

[0007] It is an object of the invention to provide a liquid crystal
display device in which a temperature of each of plural areas defined on
a liquid crystal panel can be obtained with a small number of temperature
sensors.

[0008] A liquid crystal display device according to the invention
includes: at least one temperature sensor; a liquid crystal panel having
a plurality of areas defined thereon, wherein number of the plurality of
areas is larger than that of the at least one temperature sensor; a
memory having temperature relation information stored therein in advance,
the temperature relation information being defined as information for
representing a relation between an output value of the at least one
temperature sensor and a temperature of each of the plurality of areas;
and a controller which receives an output value of the at least one
temperature sensor and estimates, based on the temperature relation
information and the received output value of the at least one temperature
sensor, a temperature of each of the plurality of areas. According to the
invention, the temperature of each of the plural areas can be obtained
with a small number of temperature sensors.

[0009] In one aspect of the invention, the controller may use a plurality
of relation formulas defined by the temperature relation information to
thereby estimate the temperatures of the plurality of areas, wherein each
of the plurality of relation formulas represents the relation between the
output value of the at least one temperature sensor and the temperature
of each of the plurality of areas. According to this aspect, a
continuously changing value can be calculated as the temperature of each
of the areas, which can increase the accuracy of estimation of
temperature. In this aspect, the memory may have a plurality of
coefficients stored therein as the temperature relation information,
wherein the plurality of coefficients is associated with the plurality of
areas respectively, and the plurality of relation formulas may be defined
by a fundamental relation formula to which the plurality of coefficients
are applied, respectively. According to this aspect, it is no more
necessary to store in the memory the plural relation formulas
respectively corresponding to the plural areas. For example, the plural
relation formulas respectively corresponding to the plural areas can be
obtained from one fundamental relationship.

[0010] In another aspect of the invention, the controller may determine,
the controller may determine, based on information changing according to
an elapsed time since the start of driving of the liquid crystal display
device, whether or not a present time falls in a steady-state period
about temperature of the liquid crystal panel, and the controller may
execute, as a process for estimating temperatures of the plurality of
areas, processes different depending on whether the present time falls in
the steady-state period or the present time does not fall in the
steady-state period. According to this aspect, even if the present time
is not the steady-state period, the temperature of the liquid crystal
panel can be properly estimated. In this aspect, two temperature sensors
disposed away from each other may be included as the at least one
temperature sensor, and the controller may use, as the information
changing according to the elapsed time since the start of driving of the
liquid crystal display device, a difference in output value between the
two temperature sensors. According to this aspect, it can be easily
determined whether or not the present time corresponds to the
steady-state period.

[0011] In still another aspect of the invention, the liquid crystal
display device may further include a backlight unit including a light
guide plate and a light source disposed at least one side of the light
guide plate. According to this aspect, especially the process for
estimating a temperature for each of the plural areas is effectively
operated. Moreover, in this aspect, the liquid crystal display device may
further include a circuit board having the at least one temperature
sensor attached thereon and disposed along the at least one side of the
light guide plate. By doing this, a correlation between the output value
of the temperature sensor and the temperature of the liquid crystal panel
can be increased. The liquid crystal display device may further include a
rear frame made of metal and covering the rear side of the backlight
unit, wherein the circuit board is fixed to the rear frame. According to
this configuration, the correlation between the output value of the
temperature sensor and the temperature of the liquid crystal panel can be
further increased. Moreover, the liquid crystal display device may
further include a plurality of circuit boards, wherein the at least one
temperature sensor is attached to one of the plurality of circuit boards
which is closest to the light source. According to this configuration,
the correlation between the output value of the temperature sensor and
the temperature of the liquid crystal panel can be further increased.
Moreover, in this aspect, the light source may include plural LEDs. When
LEDs are used in this manner, especially the process for estimating the
temperature for each of the plural areas is effectively operated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a cross-sectional view of a liquid crystal display device
related to an embodiment of the invention.

[0013]FIG. 2 is a schematic view showing the rear side of a rear frame
covering the rear side of a liquid crystal panel and a backlight unit of
the liquid crystal display device.

[0014]FIG. 3 is a schematic plan view of the circuit board illustrating
positions of the screws and temperature sensor.

[0015]FIG. 4 is a block diagram schematically showing a configuration of
the liquid crystal display device.

[0016] FIG. 5 is a block diagram showing functions of a controller of the
liquid crystal display device.

[0017]FIG. 6 is a diagram showing an example of temporal change in output
value of the temperature sensor and temporal change in actual temperature
of each area.

[0018]FIG. 7 is a diagram showing a table in which plural areas are
associated with coefficients.

[0019]FIG. 8 is a diagram showing an example of temporal changes in
output value of the temperature sensor and in temperature of each area.
In this drawing, the changes since the start of driving (time when the
power is turned on) of the liquid crystal display device are shown.

[0020] FIGS. 9A and 9B are diagrams each showing a change in temperature
of each area in a transient period. FIG. 9A shows an example of change
when the driving of the liquid crystal display device is resumed after a
long time has elapsed since the end of previous driving (when the power
is turned off) of the liquid crystal display device. FIG. 9B shows an
example of change when the driving of the liquid crystal display device
is resumed without a time interval since the end of previous driving of
the liquid crystal display device.

[0021] FIG. 10 is a diagram showing an example of a gray-scale value table
used for the correction of gray-scale value.

[0022] FIG. 11 is a diagram for explaining a method for obtaining
coefficients for estimating a temperature of each area.

[0023]FIG. 12 is a diagram showing an example of a result of temperature
measurement conducted in determining constants.

[0024]FIG. 13 is a diagram showing another example of the arrangement of
temperature detectors for measuring an actual temperature of the liquid
crystal panel.

[0025] FIG. 14 is a schematic view showing the rear side of a rear frame
included in a liquid crystal display device of another example.

DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, an embodiment of the invention will be described with
reference to the drawings. FIG. 1 is a cross-sectional view of a liquid
crystal display device 1 related to an embodiment of the invention. FIG.
2 is a schematic view of the rear side of a rear frame 31 covering the
rear side of a liquid crystal panel 10 and a backlight unit 20 included
in the liquid crystal display device 1.

[0027] The liquid crystal display device 1 is a device functioning as, for
example, a television. As shown in FIG. 1, the liquid crystal display
device 1 has the liquid crystal panel 10. The liquid crystal panel 10 has
two transparent substrates facing each other. One substrate (TFT
substrate) 10a of the substrates has plural TFTs (Thin Film Transistors)
formed thereon. The TFT substrate 10a has plural scanning lines and
plural signal lines formed thereon in a matrix form. A gate voltage for
turning on/off the TFT is applied to the scanning line. An image signal
representing a gray-scale value of each pixel is applied to the signal
line. The other substrate (color filter substrate) 10b has color filters
formed thereon. Liquid crystal 10c is sealed between the TFT substrate
10a and the color filter substrate 10b.

[0028] As shown in FIG. 1, the liquid crystal display device 1 has the
backlight unit 20 disposed on the rear side of the liquid crystal panel
10 and radiating light toward the rear face of the liquid crystal panel
10. The backlight unit 20 of this example has a light source at the edges
thereof. The backlight unit 20 has plural LEDs (Light Emitting Diodes) 21
as a light source. In this example, the plural LEDs 21 are disposed along
the lower and upper edges of the backlight unit 20. Particularly, the
backlight unit 20 has a light guide plate 22, a circuit board 21a
disposed along the lower side of the light guide plate 22, and a circuit
board (not shown) disposed along the upper side of the light guide plate
22. The LEDs 21 are mounted on the circuit board 21a and face the lower
face of the light guide plate 22. A reflector 23 is disposed on the rear
side of the light guide plate 22. Light of the LEDs 21 emitted toward the
light guide plate 22 is reflected forward by the reflector 23 while
travelling within the light guide plate 22 and radiated to the rear face
of the liquid crystal panel 10. On the front face of the light guide
plate 22, plural optical sheets 25 are disposed. The light source of the
backlight unit 20 is not limited to LED. For example, a cold-cathode tube
may be provided as a light source. Moreover, the light source may be
disposed only on one of the lower and upper sides of the light guide
plate 22.

[0029] As shown in FIG. 1, the liquid crystal display device 1 has a heat
discharging plate 24 made of metal. The heat discharging plate 24 is
disposed along the edge of the backlight unit 20 to absorb heat from the
LEDs 21, thereby preventing the heat from concentrating on the vicinity
of the LEDs 21. The heat discharging plate 24 of this example has a lower
plate portion 24a fixed to the lower face of the circuit board 21a and a
rear plate portion 24b bending at the edge of the lower plate portion 24a
and facing the rear face (particularly the rear face of the light guide
plate 22) of the backlight unit 20. The lower plate portion 24a and the
rear plate portion 24b are integrally formed. The heat discharging plate
24 has substantially the same length as the width of the backlight unit
20 in the horizontal direction (direction indicated by X1-X2 in FIG. 2).
The heat of the LEDs 21 is easily conducted to a temperature sensor 41
described later through the heat discharging plate 24.

[0030] As shown in FIG. 1, the liquid crystal display device 1 further has
the rear frame 31 made of metal. The rear frame 31 is a plate-like member
and covers the rear side of the backlight unit 20. The rear frame 31 has
a rear plate portion 31b facing the rear face (particularly the rear face
of the light guide plate 22) of the backlight unit 20 and a lower plate
portion 31a formed at the edge of the rear plate portion 31b. The lower
plate portion 31a is disposed along the lower face of the circuit board
21a. In this example, the lower plate portion 24a of the heat discharging
plate 24 is located between the lower plate portion 31a and the circuit
board 21a. The rear plate portion 24b of the heat discharging plate 24 is
located between the lowermost portion of the rear plate portion 31b and
the light guide plate 22. Therefore, the heat of the LEDs 21 is easily
conducted to the lowermost portion of the rear frame 31 through the heat
discharging plate 24.

[0031] As shown in FIGS. 1 and 2, circuit boards 12A and 12B are fixed to
the rear frame 31. The circuit boards 12A and 12B are fixed to the
lowermost portion of the rear frame 31 and located along the lower edge
of the backlight unit 20. With this configuration, the heat of the LEDs
21 is easily conducted to the circuit boards 12A and 12B. In this example
as shown in FIG. 1, the rear plate portion 24b of the heat discharging
plate 24 is located between the backlight unit 20 and the circuit boards
12A and 12B. With this configuration, the heat of the LEDs 21 is further
easily conducted to the circuit boards 12A and 12B. The rear plate
portion 24b extends upward further than the upper edge of the circuit
boards 12A and 12B. With this configuration, the heat of the LEDs 21 is
easily conducted to the wide range of the circuit boards 12A and 12B.

[0032] The liquid crystal display device 1 includes at least one
temperature sensor used for temperature estimation of the liquid crystal
panel 10. The liquid crystal display device 1 of this example includes
one temperature sensor 41 as shown in FIGS. 1 and 2. The temperature
sensor 41 is attached to the circuit board 12A.

[0033] As shown in FIG. 2, the liquid crystal display device 1 further has
a TFT control circuit board 13, a power circuit board 14, and an
application circuit board 15. In this example, all of the boards 13, 14,
and 15 are fixed to the rear frame 31. In this example, a controller 2
and a memory 3, which will be described later, are mounted on the TFT
control circuit board 13. On the application circuit board 15, a circuit
functioning as an interface to external equipment is mounted. On the
power circuit board 14, a power supply circuit which supplies driving
power to each of the circuits included in the liquid crystal display
device 1 is mounted.

[0034] The circuit board 12A to which the temperature sensor 41 is
attached and the circuit board 12B which is disposed side by side with
the circuit board 12A in the horizontal direction are circuit boards
closest to the LEDs 21, among the plural circuit boards of the liquid
crystal display device 1. In this example, the TFT control circuit board
13 is located at the central part of the rear frame 31 in the horizontal
direction and located upper to the circuit boards 12A and 12B. The power
circuit board 14 and the application circuit board 15 are disposed on the
left and right sides of the TFT control circuit board 13 and located
upper to the circuit boards 12A and 12B, respectively. Since the circuit
board 12A of the two circuit boards 12A and 12B is located away from the
power circuit board 14, the circuit board 12A is insusceptible to heat
from the power circuit board 14. On the other hand, since the circuit
board 12B is located away from the application circuit board 15, the
circuit board 12B is insusceptible to heat from the application circuit
board 15. When only one temperature sensor is used, one circuit board
which can more properly detect a temperature may be selected from the
circuit boards 12A and 12B. In the embodiment, in view of the influence
of heat from the power circuit board 14, the temperature sensor 41 is
disposed on the circuit board 12A. Therefore, an output value of the
temperature sensor 41 is insusceptible to heat from the power circuit
board 14.

[0035] A later-described process based on the output value of the
temperature sensor 41 is executed in the controller 2 mounted on the TFT
control circuit board 13. As shown in FIG. 2, the circuit boards 12A and
12B and the application circuit board 15 are connected to the TFT control
circuit board 13 through FPCs (Flexible Printed Circuits) 16 and 17. As
described above, the temperature sensor 41 is attached to the circuit
board 12A. Therefore, it is unnecessary to provide dedicated wiring for
inputting an output signal of the temperature sensor 41 to the controller
2. That is, the output signal of the temperature sensor 41 is input to
the controller 2 through the FPC 16.

[0036] As described above, the circuit board 12A is so disposed that the
heat of the LEDs 21 is easily conducted to the circuit board 12A.
Therefore, the heat of the LEDs 21 is properly reflected in the output
value of the temperature sensor 41. The temperature of the liquid crystal
panel 10 is susceptible to the heat of the LEDs 21. Due to such an
arrangement of the temperature sensor 41 and the circuit board 12A, the
accuracy of temperature estimation of the liquid crystal panel 10 using
the temperature sensor 41 can be increased.

[0037] As shown in FIG. 1, the liquid crystal display device 1 includes a
plate-like board cover 33. The board cover 33 covers the circuit boards
12A and 12B. The temperature sensor 41 is located inside the board cover
33. Therefore, the output value of the temperature sensor 41 is
insusceptible to outside air temperature. As a result, the accuracy of
temperature estimation of the liquid crystal panel 10 using the
temperature sensor 41 can be increased. The edge of the board cover 33
protrudes toward the rear frame 31. With this configuration, it is
further difficult for outside air to enter the inside of the board cover
33.

[0038] As shown in FIG. 1, the circuit board 12A is fixed to the rear
frame 31 with screws 32. FIG. 3 is a schematic plan view of the circuit
board 12A illustrating positions of the screws 32 and temperature sensor
41. In the drawing, the board cover 33 is not illustrated. As shown in
FIG. 3, the circuit board 12A is fixed to the rear frame 31 with the
plural screws 32. The screws 32 are made of metal, and part of heat of
the rear frame 31 is conducted to the circuit board 12A through the
screws 32. The position of the temperature sensor 41 is close to one of
the screws 32. Therefore, heat from the LEDs 21 can be properly reflected
in the output value of the temperature sensor 41. As shown in FIG. 1, the
screw 32 of this example is inserted from the outside of the board cover
33 and fixes not only the circuit board 12A but also the board cover 33
to the rear frame 31. The temperature sensor 41 is interposed between the
circuit board 12A and the board cover 33.

[0039] As shown in FIG. 1, the circuit boards 12A and 12B are connected to
the lower edge of the liquid crystal panel 10 through an FPC 12a. An IC
chip 12b is mounted on the FPC 12a. The IC chip 12b is located away from
the temperature sensor 41. Therefore, the temperature sensor 41 is less
exposed to heat from the IC chip 12b. In this example, the IC chip 12b is
located outside the board cover 33. Therefore, the temperature sensor 41
is much less exposed to heat from the IC chip 12b. The IC chip 12b
functions as a signal line drive circuit 4 described later. The circuit
boards 12A and 12B are each generally referred to as a source board and
each function as a junction circuit board connecting the signal line
drive circuit 4 with the controller 2. The IC chip 12b applies a voltage
according to a gray-scale value to a source of TFT.

[0040] As shown in FIG. 1, the liquid crystal display device 1 has a front
cover 51 covering the outer periphery of the liquid crystal panel 10 and
a rear cover 52 covering the rear side of the rear frame 31 and
constituting the rear face of the liquid crystal display device 1.
Further, the liquid crystal display device 1 has a middle frame 53.

[0041]FIG. 4 is a block diagram schematically showing circuits included
in the liquid crystal display device 1. As shown in the drawing, the
liquid crystal display device 1 has the controller 2, the memory 3, the
signal line drive circuit 4, a scanning line drive circuit 5, and a
backlight drive circuit 6.

[0042] An input image signal received by a not-shown tuner or antenna and
an input image signal generated by another device such as a video player
are input to the controller 2. The controller 2 includes a CPU (Central
Processing Unit), is connected to the memory 3 such as a ROM (Read Only
Memory) or RAM (Random Access Memory), and executes programs stored in
the memory 3. For example, the controller 2 generates, based on the input
image signal, an output image signal representing a gray-scale value of
each pixel and outputs the image signal to the signal line drive circuit
4. Moreover, the controller 2 generates, based on the input image signal,
a timing signal for synchronizing the signal line drive circuit 4 with
the scanning line drive circuit 5 and outputs the timing signal to each
of the drive circuits. The temperature sensor 41 is connected to the
controller 2. The controller 2 executes, based on the output value of the
temperature sensor 41, a process for estimating the temperature of the
liquid crystal panel 10. The process executed by the controller 2 will be
described later in detail.

[0043] The scanning line drive circuit 5 is connected to the scanning
lines formed on the TFT substrate 10a and applies a gate voltage in
sequence to the plural scanning lines in time with the timing signal
input from the controller 2. The scanning line drive circuit 5 is mounted
on a not-shown board disposed on, for example, the left or right side of
the liquid crystal panel 10.

[0044] The signal line drive circuit 4 is connected to the signal lines
formed on the TFT substrate 10a and applies to each of the signal lines a
voltage according to the output image signal from the controller 2 in
time with the timing of applying the gate voltage. The signal line drive
circuit 4 is mounted on the FPC 12a in the embodiment but may be mounted
on, for example, the circuit board 12A or 12B, or the TFT substrate 10a.

[0045] The backlight drive circuit 6 supplies its driving power to the
LEDs 21 based on a signal input from the controller 2. The controller 2
has, as drive modes of the backlight unit 20, plural drive modes
depending on which the luminance of the LEDs 21 varies. For example, the
controller 2 has a high luminance mode in which the LEDs 21 are driven at
high luminance, a low luminance mode in which the LEDs 21 are driven at
low luminance, and a middle luminance mode in which the LEDs 21 are
driven at middle luminance. The backlight drive circuit 6 receives a
signal representing a drive mode from the controller 2 and supplies the
LEDs 21 with driving power corresponding to the drive mode. The backlight
drive circuit 6 is mounted also on a not-shown board.

[0046] FIG. 5 is a block diagram showing functions of the controller 2. As
shown in the drawing, the controller 2 includes, as its functions, a
sensor output acquiring section 2a, a temperature estimating section 2b,
and a correction processing section 2c. The sensor output acquiring
section 2a acquires the output value of the temperature sensor 41 with a
predetermined sampling period (for example, 10 seconds). When output from
the temperature sensor 41 is an output signal in the form of analog, the
output is input as a digital signal to the controller 2 through a
not-shown A/D conversion circuit. The sensor output acquiring section 2a
acquires a value represented by the digital signal as the output value of
the temperature sensor 41. On the other hand, when the output from the
temperature sensor 41 is an output signal in the form of digital, the
sensor output acquiring section 2a acquires a value represented by the
digital signal as it is as the output value of the temperature sensor 41.

[0047] As described above, the temperature sensor 41 is attached at a
position where the temperature sensor is susceptible to heat from the
LEDs 21. Moreover, the temperature of the liquid crystal panel 10 is
strongly affected by heat from the LEDs 21. Therefore, there is a
correlation between the output value of the temperature sensor and the
temperature of the liquid crystal panel 10. The temperature estimating
section 2b estimates the temperature of the liquid crystal panel 10 based
on the output value acquired in the sensor output acquiring section 2a.

[0048] As shown in FIG. 4, plural areas A1 to A25 whose number is larger
than that of the temperature sensor 41 are defined on the liquid crystal
panel 10. That is, the total area of the liquid crystal panel 10 is
divided virtually into the plural areas A1 to A25. In the example shown
in FIG. 4, the liquid crystal panel 10 is divided into five parts in each
of the vertical and horizontal directions and has 25 areas in total. The
number of areas defined on the liquid crystal panel 10 is not limited to
that and may be appropriately changed according to the size of the liquid
crystal panel 10.

[0049]FIG. 6 is a diagram showing an example of temporal change in output
value of the temperature sensor 41 and temporal change in actual
temperature of each area. In the drawing, temperatures (measured values)
of the areas A3, A13, and A15 are shown as examples. Moreover in the
drawing, the backlight unit 20 is driven in the high luminance mode until
t1, driven in the low luminance mode from t1 to t2, and driven in the
middle luminance mode after t2. As shown in the drawing, the temperature
of any of the areas changes according to the switching of the drive mode
of the backlight unit 20. In the liquid crystal display device 1, the
LEDs 21 are disposed at the edges of the backlight unit 20. It is found
from FIG. 6 that temperature distribution occurs at each of the areas in
the liquid crystal panel 10. As shown in FIG. 1, the temperature sensor
41 is disposed at a position where the temperature of the LEDs 21 is
easily detected. Therefore as shown in FIG. 6, there is a correlation
between the output value of the temperature sensor 41 and the temperature
of each of the areas. In the example described herein, a temperature
(temperature of the area A3 in the drawing) of an area close to the
position (the upper and lower edges of the backlight unit 20 in this
example) of the LEDs 21 of the liquid crystal panel 10 is higher than
temperatures of the other areas (the area A13 and the area A15 in the
drawing). Moreover, the liquid crystal panel 10 has, on the rear side of
the right-side and left-side portions of the liquid crystal panel 10,
small number of components serving as a heat source such as a circuit
board. Therefore, a temperature of the right-side or left-side portion of
the liquid crystal panel 10 (temperature of the area A15 in the example
of the drawing) is lower than a temperature (temperature of the area A13
in the drawing) of an area at the center of the panel. A change in
temperature of the LEDs 21 is dominant over the temperature of each area
of the liquid crystal panel 10. Therefore, the tendency of change in
temperature of the areas A1 to A25 can be grasped from the output value
of the temperature sensor 41 placed at a position where the temperature
sensor is susceptible to the temperature of the LEDs 21.

[0050] In the embodiment, the memory 3 has temperature relation
information stored therein in advance and representing a relation between
the output value of the temperature sensor 41 and the temperature of each
of the areas A1 to A25. The temperature estimating section 2b estimates
the temperature of each of the plural areas A1 to A25 based on the
temperature relation information and the output value acquired in the
sensor output acquiring section 2a.

[0051] The temperature estimating section 2b uses plural relation formulas
(hereinafter, temperature relation formula(s)) defined by the temperature
relation information to estimate the temperatures of the areas A1 to A25.
The plural temperature relation formulas represent the relations between
the output value of the temperature sensor 41 and the temperatures of the
areas A1 to A25, respectively. That is, the plural temperature relation
formulas respectively correspond to the areas A1 to A25, and a relation
between a temperature of one area and an output value of the temperature
sensor 41 is represented by a temperature relation formula corresponding
to the area.

[0052] In this example, plural coefficients respectively associated with
the areas A1 to A25 are stored in the memory 3. A temperature relation
formula for one area is defined by coefficients corresponding to the
area. Moreover in this example, a fundamental relation formula to which
the plural coefficients associated with each of the areas A1 to A25 can
be applied selectively is stored in the memory 3. The fundamental
relation formula is a formula serving as a source of the temperature
relation formula for each of the areas, and coefficients corresponding to
each area are applied to the fundamental relation formula, whereby a
temperature relation formula for a relevant area can be obtained.

T is a temperature estimated for any of the areas. Td(i) is a latest
output value acquired by the sensor output acquiring section 2a. K, R and
OFS are constants. Specifically, K and R are coefficients, and OFS is an
offset value. When a temperature of each area is calculated, specific
constants corresponding to the area are applied. For example, when the
temperature of the area A1 is calculated, constants (KA1, RA1,
OFSA1) associated with the area A1 are applied to the constants K,
R, and OFS in the above expression (1). A function F is a filter function
which outputs a value reflecting an output value acquired before the
latest output value.

Td(i-1) is an output value acquired at the previous process by the sensor
output acquiring section 2a. H is a filter coefficient. When a
temperature of each area is calculated, a specific coefficient
corresponding to the area is applied. For example, when the temperature
of the area A1 is calculated, a coefficient (HA1) associated with
the area A1 is applied to the coefficient H. Since the fundamental
relation formula includes the filter function, a value output by the
temperature relation formula is based not only on the latest output value
of the temperature sensor 41 but also on at least the output value
acquired at the previous process. This makes it possible to compensate a
lag between a change of the output value of the temperature sensor 41 and
a change of the actual temperature of the liquid crystal display panel
10. Further, this makes it possible to prevent a temperature calculated
by the temperature estimating section 2b from following an instantaneous
change or noise in output value acquired by the sensor output acquiring
section 2a. The function F is not limited to the IIR filter. The function
F may be, for example, a FIR filter (Finite Impulse Response Filter).

[0055] As shown by Expression (1), the temperature relation formula
defined by the fundamental relation formula and the constants associated
with each of the areas is a first order filter function for the output
value of the temperature sensor 41. Therefore, the processing load of
temperature estimation can be reduced. The temperature relation formula
is not limited to that described above. For example, the temperature
relation formula may be a second order filter function or third order
filter function for the output value of the temperature sensor 41.

[0056] As described above, the temperature relation formula is defined by
the plural constants (hereinafter referred to as constant group)
associated with the areas A1 to A25. For example, the temperature
relation formula for the area A1 is defined by a constant group
(KA1, RA1, OFSA1, and HA1). In this example, a table
(hereinafter, constant table) which associates areas with constant
groups, respectively, shown in FIG. 7, is stored in the memory 3.

[0057] In this embodiment where such temperature relation information is
stored in the memory 3, the temperature estimating section 2b executes
the following process for estimating the temperature of each area. In the
process for estimating the temperature of an area Am (m=1, 2, . . . , and
25 in this example), the temperature estimating section 2b first refers
to the constant table to select a constant group corresponding to the
area Am. Then, the temperature estimating section 2b uses a fundamental
relation formula to which the selected constant group is applied, that
is, a temperature relation formula representing a relation between the
output value of the temperature sensor 41 and the temperature of the area
Am to calculate the temperature of the area Am from the output value
acquired by the sensor output acquiring section 2a. The temperature
estimating section 2b executes the process described above for each area
to estimate the temperatures of all the areas A1 to A25. The temperature
estimating section 2b executes the process described above with a
predetermined period (for example, the same period as the sampling period
of the sensor output acquiring section 2a) to calculate the temperatures
of the areas A1 to A25.

[0058] The process executed by the temperature estimating section 2b and
the information stored in the memory 3 is not limited to that described
above. For example, plural temperature relation formulas respectively
associated with the areas A1 to A25 may be previously stored in the
memory 3 as temperature relation information. Moreover, plural tables
representing temperatures of the areas A1 to A25 may be stored in the
memory 3 respectively in association with plural output values which can
be output by the temperature sensor 41. In this case, the temperature
estimating section 2b reads from the memory 3 a table corresponding to an
output value acquired in the sensor output acquiring section 2a. Then,
the temperature estimating section 2b defines temperatures which are set
in the read table as estimated temperatures of the areas A1 to A25.

[0059] The relation between the output value of the temperature sensor 41
and the temperature of the liquid crystal panel 10 varies depending on an
elapsed time since the start of driving (when the power is turned on) of
the liquid crystal display device 1. After a sufficient time has elapsed
since the start of driving, there is the correlation, illustrated in FIG.
6, between the temperature of each of the areas and the output value of
the temperature sensor 41. However, under the situation where the liquid
crystal display device 1 is not driven, both of a temperature in the
vicinity of the temperature sensor 41 and the temperature of each area
depend on the temperature of an environment where the liquid crystal
display device 1 is placed, and are substantially equal to each other.
Therefore, until a sufficient time has elapsed since the start of driving
of the liquid crystal display device 1, the temperature of each of the
areas and the output value of the temperature sensor 41 sometimes do not
have the relation represented by the temperature relation formula
described above.

[0060]FIG. 8 is a diagram showing an example of temporal changes in
output value of the temperature sensor 41 and in temperature of each
area. In the drawing, the changes since the start of driving of the
liquid crystal display device 1 are shown. Moreover in the drawing,
temperatures of the areas A3, A13, and A15 are shown as examples. In the
case shown in the drawing, the backlight unit 20 is driven in the high
luminance mode from the start of driving when the power is turned on to
t1, driven in the low luminance mode from t1 to t2, and driven in the
middle luminance mode after t2. As shown in the drawing, after a
sufficient time has elapsed (that is, in a steady-state period shown in
the drawing) since the start of driving of the liquid crystal display
device 1, there is a high correlation represented by the temperature
relation formula described above. However, until a sufficient time has
elapsed (that is, in a transient period shown in the drawing) since the
start of driving of the liquid crystal display device 1, a relation
between the temperature of each of the areas and the output value of the
temperature sensor 41 is not similar to that of the steady-state period,
and a difference between the temperature of each of the areas and the
output value of the temperature sensor 41 is gradually increased over
time.

[0061] Therefore, the temperature estimating section 2b may determine,
based on information changing according to the elapsed time since the
start of driving of the liquid crystal display device 1, whether or not a
present time falls to the steady-state period. Then, the temperature
estimating section 2b may estimate the temperatures of the areas A1 to
A25 by a process different depending on whether or not the present time
falls to the steady-state period.

[0062] The process for determining whether or not the present time falls
to the steady-state period is executed as follows, for example. The
temperature estimating section 2b initiates timing at the start of
driving of the liquid crystal display device 1 and determines, based on
the elapsed time since the start of driving, whether or not the present
time has reached the steady-state period. That is, the temperature
estimating section 2b determines that the present time has reached the
steady-state period when the elapsed time since the start of driving
exceeds a predetermined time. Moreover as shown in FIG. 8, the output
value of the temperature sensor 41 abruptly changes immediately after the
start of driving of the liquid crystal display device 1. Therefore, the
temperature estimating section 2b may determine, based on the rate of
change in output value of the temperature sensor 41, whether or not the
present time falls to the steady-state period. For example, the
temperature estimating section 2b may determine, based on differences
each defined as a difference between two output values acquired with a
predetermined period, whether or not the present time falls to the
steady-state period. If the difference is smaller than a threshold value,
the present time may be determined as falling to the steady-state period.

[0063] If the present time falls to the steady-state period, the
temperature estimating section 2b uses the constant group and fundamental
relation formula described above to estimate the temperature of each
area. On the other hand, if the present time does not fall to the
steady-state period, that is, if the present time falls to the transient
period, the temperature estimating section 2b uses, for example, a
constant group different from the constant group described above and/or a
relation formula different from the fundamental relation formula
described above to estimate the temperature of each area. In this case,
the memory 3 has temperature relation information stored therein which
represent a relation between the output value of the temperature sensor
41 and the temperature of each area in the transient period and which is
different from the temperature relation information described above to be
used in the steady-state period. Also the temperature relation
information in the transient period is composed of, for example, a
fundamental relation formula and a constant group associated with each
area. As another example, in the transient period, the temperature
estimating section 2b may correct a value calculated using the constant
group and fundamental relation formula described above and define the
corrected value as the temperature of each area in the transient period.
In this case, the temperature estimating section 2b may correct the value
obtained from the constant group and the fundamental relation formula
described above used in the steady-state period based on, for example,
the rate of change in output value of the temperature sensor 41.

[0064] FIGS. 9A and 9B are diagrams each showing a change in temperature
of each area in the transient period. In the case shown in those
diagrams, changes in temperature of the areas A3, A13, and A15 are shown
as examples. FIG. 9A shows an example of change in the case where the
driving of the liquid crystal display device 1 is resumed after along
time has elapsed since the end of previous driving (when the power is
turned off). FIG. 9B shows an example of change in the case where the
driving is resumed without a sufficient time interval since the end of
previous driving. When a long time has elapsed since the end of driving,
a temperature in the vicinity of the temperature sensor 41 and the
temperature of each area are equal to each other. Therefore as shown in
FIG. 9A, at the start of driving after a long time has elapsed,
temperatures of all areas are equal to each other. In a case where only a
short time has elapsed, however, differences in temperature among the
areas are not eliminated. Therefore, when the driving is resumed without
a sufficient time interval after the end of previous driving, the
differences in temperature among the areas already exist at the start of
driving of the liquid crystal display device 1 as shown in FIG. 9B.

[0065] Therefore, the temperature estimating section 2b may change, based
on information changing according to the elapsed time since the end of
previous driving, the constant group and/or fundamental relation formula
used in the transient period. This process can be executed, for example,
as follows.

[0066] The temperature estimating section 2b stores, at the end of driving
of the liquid crystal display device 1, the output value of the
temperature sensor 41 in the memory 3. Thereafter, when the driving is
resumed, the temperature estimating section 2b may determine, based on a
difference between the output value of the temperature sensor 41 acquired
at the start of driving and the output value stored in the memory 3 at
the end of previous driving, whether or not a sufficient time has elapsed
since the end of previous driving. For example, if the difference between
the output value of the temperature sensor 41 acquired at the start of
driving and the output value stored in the memory 3 at the end of
previous driving is larger than a threshold value, the temperature
estimating section 2b determines that a sufficient time has elapsed since
the end of previous driving. The temperature estimating section 2b may
change the constant group and/or fundamental relation formula used in the
transient period after the start of driving depending on whether or not a
sufficient time has elapsed since the end of previous driving.

[0067] The correction processing section 2c corrects various kinds of
parameters related to an image to be displayed on the liquid crystal
panel 10. The correction processing section 2c calculates parameters
related to an image to be displayed in an area Am of the plural areas A1
to A25 based on a temperature estimated for the area Am. The parameters
are, for example, gray-scale values of pixels formed on the TFT substrate
10a or voltages to be applied to a common electrode (not shown) formed on
the TFT substrate 10a or the color filter substrate 10b. That is, in one
example, the correction processing section 2c corrects, based on the
estimated temperature, a gray-scale value calculated from an input image
signal and outputs a signal corresponding to the corrected gray-scale
value as an output image signal (such a correction is executed as for
example, a correction for eliminating crosstalk between two successive
frames). In another example, the correction processing section 2c
corrects the voltages to be applied to the plural electrodes provided at
the edge of the common electrode based on temperatures of the areas A1 to
A25 (Vcom correction).

[0068] Herein, the correction processing section 2c which corrects
gray-scale values will be described as an example. The correction
processing section 2c corrects the gray-scale values of pixels formed in
an area Am based on a temperature estimated for the area Am. As shown in
FIG. 5, the correction processing section 2c includes a gray-scale value
table selecting section 2d and a gray-scale value calculating section 2e.

[0069] The gray-scale value calculating section 2e calculates, based on a
gray-scale value of a previous frame and a gray-scale value (gray-scale
value before correction) according to an input image signal of a next
frame, a gray-scale value (gray-scale value after correction) of the next
frame and outputs a signal corresponding to the calculated gray-scale
value as an output image signal. The memory 3 has a table stored therein
in which candidates for gray-scale values calculated by the gray-scale
value calculating section 2e. In the gray-scale value table, the
gray-scale value of the next frame is set in association with the
gray-scale value of the previous frame and the gray-scale value according
to the input image signal of the next frame. The memory 3 has plural
gray-scale value tables stored therein which are in association with
temperatures. The gray-scale value table selecting section 2d selects the
gray-scale value table based on a temperature calculated in the
temperature estimating section 2b for each area. That is, the gray-scale
value table selecting section 2d selects the gray-scale value table for
each of the plural areas A1 to A25.

[0070] FIG. 10 is a diagram showing an example of a gray-scale value
table. In the table in the diagram, gray-scale values according to the
input image signals of the next frame are shown in the top row.
Gray-scale values set in the previous frame are shown in the leftmost
column. In the memory 3, such plural gray-scale value tables are stored
in association with temperatures (refer to FIG. 5).

[0071] When the temperature estimating section 2b calculates a temperature
for each of the areas A1 to A25, the gray-scale value table selecting
section 2d selects, based on each of the temperatures, the gray-scale
value table for each of the plural areas A1 to A25. Then as shown in FIG.
5, the gray-scale value table selecting section 2d stores the selected
gray-scale value tables, in association with the areas A1 to A25, in a
memory area defined previously within the memory 3. That is, after
selecting the gray-scale value table based on the temperature of an area
Am, the gray-scale value table selecting section 2d stores the selected
gray-scale value table in the memory 3 in association with the area Am.
When a new temperature is calculated in the temperature estimating
section 2b, the gray-scale value table selecting section 2d selects the
gray-scale value table based on the new temperature and updates the
gray-scale value table which has been already stored to the newly
selected gray-scale value table.

[0072] The gray-scale value calculating section 2e calculates the
gray-scale values of pixels in each area with reference to the gray-scale
value table associated with a relevant area. That is, when calculating
the gray-scale value of one pixel, the gray-scale value calculating
section 2e selects a gray-scale value table associated with an area
including the pixel. Then, the gray-scale value calculating section 2e
refers to the selected gray-scale value table to calculate a gray-scale
value corresponding to a gray-scale value set for the pixel in the
previous frame and a gray-scale value of the pixel according to the input
image signal for the next frame. The gray-scale value calculating section
2e executes the process described above for all pixels in one frame.

[0073] In the gray-scale value table, all values from a minimum gray-scale
value (0 in FIG. 10) to a maximum gray-scale value (255 in FIG. 10) may
be defined as the gray-scale values in the previous frame and the
gray-scale values according to the input image signals for the next
frame. Moreover, like the gray-scale value table shown in FIG. 10, the
gray-scale values in the previous frame and the gray-scale values
according to the input image signals for the next frame may be set
stepwise from the minimum gray-scale value to the maximum gray-scale
value. That is, a difference larger than 1 may be provided between two
successive gray-scale values. In using the gray-scale value table in FIG.
10, when a gray-scale value in the previous frame or a gray-scale value
according to the input image signal for the next frame is a value between
two successive gray-scale values, the gray-scale value calculating
section 2e executes an interpolation process which interpolates a value
between two successive gray-scale values.

[0074] A method for obtaining constants used for the temperature
estimation of the areas A1 to A25 in manufacturing process of the liquid
crystal display device 1 will be described. FIG. 11 is a diagram for
explaining the arrangement of temperature detectors 51 used in obtaining
the constants. First, the temperature detector 51 (for example, a
thermocouple) is disposed at plural positions (25 positions in this
example) on the surface of the liquid crystal panel 10. For example as
shown in FIG. 11, one temperature detector 51 is provided in each of the
areas A1 to A25. Then, the liquid crystal display device 1 is driven
while changing the drive mode of the backlight unit 20 in plural
temperature environments. For example, the drive mode (the high luminance
mode, the middle luminance mode, and the low luminance mode) of the
backlight unit 20 is changed in order in an environment of 0 degree, and
thereafter the drive mode of the backlight unit 20 is changed in another
temperature environment. At that time, an actual temperature is measured
by the temperature detector 51 provided on the liquid crystal panel 10 at
a fixed time interval (for example, an interval of 10 seconds), and the
output value of the temperature sensor 41 is acquired at the fixed time
interval. FIG. 12 illustrates temporal changes in output value of the
temperature sensor 41 and in measured temperature obtained by the
temperature detector 51. With the temperature measurement described
above, as shown in FIG. 12, a number of measured temperatures for each
position (temperature measurement position) at which a temperature
detector 51 is attached and the output values of the temperature sensor
41 respectively corresponding to the measured temperatures are obtained.
Then, an approximate expression between a measured temperature and the
output value of the temperature sensor 41 is obtained. When one
temperature detector 51 is provided in each area, that is, when one
temperature measurement position corresponds to one area, an approximate
expression for an area Am including constant KAm, RAm,
HAm, and OFSAm is obtained from the output value of the
temperature sensor 41 and a measured temperature at a temperature
measurement position provided in the area Am. An estimated temperature
corresponding to a temperature measurement position is deemed, in the
process of the temperature estimating section 2b, as an estimated
temperature of the entire of an area including the temperature
measurement position. Specifically, the estimated temperature of an area
Am is represented by the estimated temperature at the temperature
measurement position provided in the area Am. The derivation of the
approximate expression can be carried out by, for example, the method of
least squares. That is, a value which minimizes the sum of the squares of
the difference between the temperature (temperature obtained from
Expression (1)) of an area Am based on the output value of the
temperature sensor 41 and the measured temperature of the area Am is
defined as constants for the area Am. In the case where the constants are
derived in this manner, a temperature estimation error can be reduced
when the drive mode of the backlight unit 20 is changed.

[0075] The provision of temperature measurement positions is not limited
to that described above. For example, plural temperature detectors 51 may
be provided in each area. That is, plural temperature measurement
positions may be associated with one area. In the example shown in FIG.
13, a temperature measurement position is provided at the corners of each
area, and four temperature measurement positions are associated with one
area. When the temperature measurement positions are provided in this
manner, an actual temperature of one area Am is calculated from measured
temperatures at plural temperature measurement positions associated with
the area Am. For example, the average value of the measured temperatures
at the plural temperature measurement positions is used as the actual
temperature of the area Am. Then, for the area Am, the output value of
the temperature sensor 41 and the calculated temperature of the area Am
are used to obtain an approximate expression including the coefficients
KAm, RAm, HAm, and OFSAm.

[0076] As described above, the temperature relation information
representing the relation between the output value of the temperature
sensor 41 and the temperature of each of the plural areas A1 to A25
defined on the liquid crystal panel 10 is stored in the memory 3 in
advance. The controller 2 acquires the output value of the temperature
sensor 41 and estimates the temperature of each of the areas A1 to A25
based on the temperature relation information and the acquired output
value. Therefore, it is possible to obtain the temperature of each of the
plural areas A1 to A25 defined on the liquid crystal panel 10 with a
small number of temperature sensors.

[0077] The invention is not limited to the liquid crystal display device 1
described above but can be modified variously.

[0078] For example, in the liquid crystal display device 1 described
above, one temperature sensor 41 is provided. However, many more
temperature sensors may be provided in the liquid crystal display device
1.

[0079] FIG. 14 is a rear side view of the rear frame 31 included in a
liquid crystal display device of this example. In this drawing, the same
reference and numeral signs are assigned to the same portions as those
described so far. Hereinafter, only the differences from the liquid
crystal display device 1 described so far will be described, and the
matters not described herein are similar to those of the liquid crystal
display device 1.

[0080] The liquid crystal display device shown in FIG. 14 includes plural
temperature sensors 41, 42, 43, and 44 which are disposed away from each
other. Also in this example, the number of areas defined on the liquid
crystal panel 10 is larger than the number of temperature sensors. The
temperature sensor 42 is attached to the circuit board 12B attached at
the lower edge of the rear frame 31. The temperature sensor 41 and the
temperature sensor 42 are located away from each other in a direction
along the lower edge of the rear frame 31. The temperature sensor 43 is
attached to the TFT control circuit board 13. The temperature sensor 44
is attached to the application circuit board 15. Output signals of the
sensors 41 to 44 are input to the controller 2 directly or indirectly. In
the example of the drawing, the outputs of the temperature sensors 41,
42, and 43 are directly input to the controller 2, while the output of
the temperature sensor 44 is input to the controller 2 through an IC chip
15a mounted on the application circuit board 15. In the liquid crystal
display device, many more temperature sensors may be provided. For
example, plural (for example, three) temperature sensors located away
from each other so as to surround the controller 2 may be provided on the
TFT control circuit board 13.

[0081] In this example, temperature relation information representing a
relation between the output values of the plural temperature sensors 41
to 44 and the temperature of each of the plural areas A1 to A25 are
stored in the memory 3 in advance. For example, a fundamental relation
formula serving as a source of temperature relation formulas for the
areas A1 to A25 and plural constant groups respectively associated with
the areas A1 to A25 are stored in the memory 3 as the temperature
relation information. The temperature estimating section 2b uses the
temperature relation formula defined by the constant group corresponding
to each area to calculate the temperature of a relevant area based on the
output values of the plural temperature sensors 41 to 44.

[0082] The fundamental relation formula of this example is expressed by,
for example, Expression (3).

Td1(i), Td2(i), Td3(i), and Td4(i) are the latest output values of the
temperature sensors 41, 42, 43, and 44, respectively. K1 to K4, R1 to R4,
H1 to H4, and OFS are constants. When the temperature of each area is
calculated, specific constants corresponding to a relevant area are
applied. For example, when the temperature of an area Am is calculated
(m=1, 2, . . . , and 25), constants (K1Am to K4Am, R1Am to
R4Am, H1Am to H4Am, and OFSAm) associated with the
area Am are applied to the constants K1 to K4, R1 to R4, H1 to H4, and
OFS of Expression (3). F is a filter function similar to that shown in
Expression (2) and defined by the filter coefficients H1 to H4.

[0083] As shown by Expression (3), the temperature relation formula of
this example is a first order filter function of the output values of the
temperature sensors 41, 42, 43, and 44. Therefore, the processing load of
temperature estimation is reduced. The temperature relation formula is
not limited to that. For example, the temperature relation formula may be
a second order filter function or a third order filter function of the
output value of any of the temperature sensors.

[0084] The plural constant groups respectively associated with the areas
A1 to A25 and the fundamental relation formula (3) to which the plural
constant groups can be applied selectively are stored in the memory 3 in
advance. The constant groups are also stored in the memory 3 in
association with the areas, similarly to the constant table described
with reference to FIG. 7.

[0085] Even when the temperature relation information described above is
stored in the memory 3, the process executed by the sensor output
acquiring section 2a and the temperature estimating section 2b is similar
to the form described above. That is, the sensor output acquiring section
2a acquires the output values of the temperature sensors 41, 42, 43, and
44 with a predetermined sampling period. In the process for estimating
the temperature of an area Am, the temperature estimating section 2b
first selects a constant group corresponding to the area Am from the
plural constant groups. Then, the temperature estimating section 2b uses
a temperature relation formula defined by the selected constant group and
the fundamental relation formula shown by Expression (3) to calculate the
temperature of the area Am from the output values of the plural
temperature sensors 41, 42, 43, and 44. The temperature estimating
section 2b executes the process described above for all the areas A1 to
A25.

[0086] When the plural temperature sensors 41, 42, 43, and 44 are provided
in the liquid crystal display device like this example, the temperature
estimating section 2b may determine, by the following process, whether or
not a sufficient time has elapsed since the end of previous driving of
the liquid crystal display device, that is, whether or not a present time
falls to the steady-state period.

[0087] If a sufficient time has elapsed since the end of previous driving
of the liquid crystal display device, the output values of the
temperature sensors 41, 42, 43, and 44 become values depending on
environmental temperature and are equal to each other. The temperature
sensors 41, 42, 43, and 44 are different from each other in attachment
position or distance from the LEDs 21. That is, the temperature sensors
41, 42, 43, and 44 are different from each other in conductivity of heat
of the LEDs 21. Therefore, in the steady-state period, differences are
generated in the output values of the temperature sensors 41, 42, 43, and
44. Therefore, the temperature estimating section 2b determines that a
present time falls to the steady-state period if a difference in output
value between any two of the temperature sensors is larger than a
threshold value. That is, the temperature estimating section 2b may use,
as information changing according to the elapsed time since the start of
driving of the liquid crystal display device, the difference in output
value between two temperature sensors. For example, if a difference
between the output value of a temperature sensor (the temperature sensor
41 or 42 in this example) provided at a position most susceptible to heat
from the LEDs 21 and the output value of another temperature sensor (the
temperature sensor 43 or 44 in this example) located away from the
temperature sensor mentioned before is larger than a threshold value, the
temperature estimating section 2b may determine that the present time
falls to the steady-state period.

[0088] A method for obtaining the constants associated with each of the
areas A1 to A25 in a manufacturing process of the liquid crystal display
device is similar to that described above. That is, the liquid crystal
display device is driven while changing the drive mode of the backlight
unit 20 in plural temperature environments. At that time, an actual
temperature of each of the areas A1 to A25 of the liquid crystal panel 10
is measured with a fixed time interval, and the output values of the
temperature sensors 41, 42, 43, and 44 are acquired. Then, the output
values of the temperature sensors 41, 42, 43, and 44 are used to obtain
an approximate expression for the measured temperature.

[0089] While there have been described what are at present considered to
be certain embodiments of the invention, it will be understood that
various modifications may be made thereto, and it is intended that the
appended claims cover all such modifications as fall within the true
spirit and scope of the invention.

Patent applications by Hidefumi Ishibashi, Osaka JP

Patent applications by Masahiro Ishii, Chiba JP

Patent applications by Masato Ishii, Tokyo JP

Patent applications by Toshikazu Koudo, Hyogo JP

Patent applications by Panasonic Liquid Crystal Display Co. Ltd.

Patent applications in class Detector of liquid crystal temperature

Patent applications in all subclasses Detector of liquid crystal temperature